In recent years, technologies have been developed for utilizing a variety of energy resources from a viewpoint of the environmental measure, saving resources and saving energy. Among them is a technology for taking out the mechanical energy from the thermal energy present in the natural world, such as solar heat. Technologies have also been developed to improve thermal efficiency of an internal combustion engine by recovering the power which is generated by utilizing the exhaust heat wasted into the exhaust gas or into the cooling water of an internal combustion engine such as diesel engine and the like.
Heat engines are used for converting the thermal energy into the mechanical energy such as rotational energy. Heat engines such as the internal combustion engine and the steam turbines that use an ordinary fuel such as petroleum, natural gas or the like, are the ones in which the fuel is burned to produce an operation fluid of a high temperature and a high pressure and the thermal energy is converted into the mechanical energy, and feature a high thermal efficiency since the mechanical energy is taken out from the heat source in the state of a high temperature. However, the temperature of the thermal energy in the natural world and the exhaust heat of the internal combustion engine are, usually, not so high, i.e., these are the thermal energy in a low-temperature state. In order to efficiently take out the mechanical energy from such heat sources, therefore, it becomes necessary to use a heat engine adapted to the heat source in a low-temperature state.
The engine disclosed in JP-A-2001-20706 is a heat engine for generating the mechanical energy from the heat source in a low-temperature state. As shown in FIG. 3, this engine comprises a steam-generating portion 101 and a cooling portion 102 which are coupled together through nozzles 103. A turbine 106 is arranged in the cooling portion 102 at a position facing the nozzles 103, and rotates together with magnets 107. On the inside of the magnets 107, a stationary generating coil 110 is arranged facing thereto, and the magnets 107 and the generating coil 110 together constitute a generating device. The steam-generating portion 101 and the cooling portion 102 are sealed, respectively. Water 104 which is an operation fluid is filled therein, and the air inside is evacuated by a vacuum pump. Many heat pipes 105 for heat radiation are mounted on the upper side of the cooling portion 102.
The steam-generating portion 101 and the cooling portion 102 as a whole constitute a heat pipe, and water 104, which is heated in the steam-generating portion 101 from the lower side thereof and becomes steam, creates a high-speed stream which is jetted to the blades of the turbine 106 from the nozzles 103. Accordingly, the turbine 106 and the magnets 107 rotate to produce the rotational energy which is, finally, converted into the electric energy by the magnets 107 and the generating coil 110, and is output to an external unit. The steam after having driven the turbine 106 is cooled down with the heat-radiating action of the heat pipes 105 and returns back to water. The condensate falls down to the lower side of the cooling portion 102 due to gravity, and is refluxed into the steam-generating portion 101 through the central portion.
The heat pipe that utilizes vaporization and condensation of liquid contained in the sealed container is, usually, used as a heat conveying means, i.e., as a heat transfer device. Here, the steam of liquid contained in the heat pipe moves accompanying large velocity energy and, therefore, the power can be taken out therefrom as described above. In this case, the mechanical energy can be taken out from the heat source in a low-temperature state.
The turbine disclosed in the above JP-A-2001-20706 is a so-called velocity type engine which utilizes the velocity energy of the operation fluid. To efficiently operate the turbine, the rotational speed of the turbine must be increased so that the circumferential velocity thereof is increased to match the velocity of the steam. However, when decreasing the diameter of the turbine to miniaturize it, the rotational speed of the turbine becomes very high and a large centrifugal force acts on the turbine and may beak it down. To drive the load by using an engine which revolves at high speeds, further, it becomes necessary to provide a reduction gear to lower the rotational speed. When it is attempted to take out the power in the form of electric energy by a generator, a peripheral control unit being necessary for the high speed generator are complex and expensive. Further, when the temperature of the heating portion is low and the steam is of a low temperature, the superheat of the steam is in low degree, and water droplets tend to form due to the cooling. Water droplets that are formed come into collision with the turbine blades at high speeds, and the so-called erosion is developed on the turbine blades due to the collision of water droplets.
When the heat engine is rotated being contained in a closed container, the rotary shaft must be supported by bearings having sealing performance. To support the rotary shaft that rotates at high speeds such as of the turbine, precision bearings are necessary. Namely, complex and expensive bearings must be used to support the rotary shaft maintaining sealing performance, thus requiring an increased cost for the maintenance.
The assignment of the present invention is to provide a heat engine capable of obtaining the mechanical energy not only from the heat sources of high temperatures but also from various heat sources in a low-temperature state, such as exhaust heat by an internal combustion engine while solving the above-mentioned problems inherent in the conventional heat engines.